Inks used in inkjet recording are commonly composed of water-soluble organic solvents (humectants, etc.), surfactants, and colorants in a predominantly aqueous fluid. When a recording is made on xe2x80x9cplain paperxe2x80x9d, the deposited colorants retain some mobility, which can be manifest in bleed, poor edge acuity, feathering, and inferior optical density/chroma (due to penetration of the paper). These features adversely impact text and image quality. Furthermore, when aqueous inkjet ink is printed on media designed for offset printing, problems arise because of the low absorbency of the offset media.
The evaporation rate of water-based inks is low and they dry primarily by the absorption into paper. The absorption time of an ink is dependent on many factors, such as the ink drop size, paper pore size, ink viscosity, and the ink spreading coefficient over the paper (that is, the surface tension of the paper minus the surface tension of inks and the interfacial tension of the paper-ink interface). There is a considerable interest in reducing the ink drying time, in particular, for high throughput printers. However, shortening the drying time is normally attained at the expense of the image quality. Thus, adding surfactants to inks can significantly reduce the penetration time. This however decreases the optical density/chroma and the edge acuity of the image, as well as ultimately leading to strikethrough problems, because of the penetration of the colorants in normal and lateral directions of the paper.
To address these problems, methods have been developed in which a xe2x80x9cfixerxe2x80x9d solution, with components to reduce colorant mobility, is deposited on the paper prior to depositing the ink. This xe2x80x9cunder-printingxe2x80x9d of imaging ink uses compositions containing acids, salts, and organic counter ions and polyelectrolytes. Underprinting is defined as applying a transparent liquid on paper just before applying inks. The idea is to apply xe2x80x9ca separate reactive componentxe2x80x9d before the inks in order to improve waterfastness. The xe2x80x9creactive componentxe2x80x9d reacts with the colorant present in the inks, producing an insoluble reactant-colorant complex and makes the printed image waterfast.
Underprinted fixer solutions have been used to improve aqueous inkjet ink color saturation, edge acuity and durability of inkjet printed images.
In other disclosures, the underprinting idea has been further developed. For example, using a cationic xe2x80x9cliquid compositionxe2x80x9d such as a polyallylamine for underprinting of anionic dyes has been used to achieve a fixer which reacts broadly with dye based systems as a whole.
A broad class of underprinting liquids for polymer dispersed pigments has also been disclosed, including polymer latexes, silica, alumina and titanium oxide particles, polymer resins, buffer solutions, and inorganic salts. All these underprinting liquids destabilize the pigment dispersions by various mechanisms. As a result, the pigment substantially precipitates at the surface of the paper, while the vehicle is quickly absorbed.
Another system has been described that uses water-soluble dyes and an underprinting fixer. The fixer contains ligand-complexed metal ions (metal ion with an associated ligand). The ink used in this system contains an anionic component, which may be the dye itself. The ink may also contain a polymeric viscosity modifier. The specific polymeric viscosity modifier can be an ethylene oxide adduct of acetylene glycolxe2x80x94a neutral polymer which unlike the present invention does not interact strongly with the fixer.
In one embodiment, the present invention relates to an ink-jet printing apparatus, comprising:
at least one printhead portion including a fixer fluid comprising a colorant precipitating component selected from at least one of the group consisting of cationic polymer, cationic multivalent metal salts and cationic surfactant, and at least one printhead portion including an inkjet ink comprising a colorant selected from the group consisting of anionic dyes and anionic pigments;
wherein, before the inkjet ink is printed onto a zone of a medium, a layer of the fixer fluid is underprinted and at least partially dried onto the zone to be inkjet printed, and after the inkjet ink is printed onto the zone, a fixer fluid is overprinted and at least partially dried onto the zone.
In another embodiment, the invention relates to an underprinting fixer fluid comprising a colorant precipitating component selected from at least one of the group consisting of cationic polymer, cationic multivalent metal salts and cationic surfactant,
wherein, after a layer of the underprinting fixer fluid is applied onto a zone to be inkjet printed on a medium and before inkjet printing an image onto the zone, the layer of underprinting fixer fluid is at least partially dried.
In yet another embodiment, the present invention relates to an overprinting fixer fluid comprising a colorant precipitating component selected from at least one of the group consisting of cationic polymer, cationic multivalent metal salts and cationic surfactant,
wherein, after inkjet printing an image onto a zone of the medium, a layer of the overprinting fixer fluid is applied onto the zone and the layer of the overprinting fixer fluid is at least partially dried.
In still another embodiment, the present invention relates to an inkjet ink comprising a colorant selected from the group consisting of anionic dyes and anionic pigments;
wherein, before the inkjet ink is printed onto a zone of a medium, a layer of an underprinting fixer fluid is applied and at least partially dried onto the zone to be inkjet printed, the underprinting fixer fluid comprising a colorant precipitating component selected from at least one of the group consisting of cationic polymer and cationic surfactant, and after the inkjet ink is printed onto the zone, an overprinting fixer fluid is applied and at least partially dried onto the zone, the overprinting fixer fluid comprising a colorant precipitating component selected from at least one of the group consisting of cationic polymer, cationic multivalent metal salts and cationic surfactant.
In again another embodiment, the present invention relates to a method of ink-jet printing, the method comprising the steps of:
a) applying a layer of an underprinting fixer fluid onto a zone to be inkjet printed on a medium, the underprinting fixer fluid comprising a colorant precipitating component selected from at least one of the group consisting of cationic polymer, cationic multivalent metal salts and cationic surfactant;
b) at least partially drying the layer of underprinting fixer fluid;
c) inkjet printing an image onto the dried layer of underprinting fixer fluid on the zone;
d) at least partially drying the inkjet printed image;
e) applying a layer of an overprinting fixer fluid over the zone on the medium, the overprinting fixer fluid comprising a colorant precipitating component selected from at least one of the group consisting of cationic polymer, cationic multivalent metal salts and cationic surfactant; and
f) at least partially drying the layer of overprinting fixer fluid.